docs: def attribs_to_string(attrib_dict, keys):
      """
      A more specific version of the subdict utility aimed at handling
      node and edge attribute dictionaries for NetworkX file formats such as
      gexf (which does not allow attributes to have a list type) by making
      them writable in those formats
      """
      for key, value in attrib_dict.iteritems():
          if (isinstance(value, list) or isinstance(value, dict) or
              isinstance(value, tuple)):
              attrib_dict[key] = value
  
      return attrib_dict